1. Field of the Invention:
This invention relates to an eye fundus camera used for observing and/or photographing an eye fundus to be tested or subject's retina by projecting illuminating beam thereto.
2. Description of the Prior Art:
As an eye fundus camera of this type, there is one of a laser beam scanning type for example. As this laser beam scanning type eye fundus camera, there can be considered one which includes an illuminating optical system for scanning laser beam, which is emitted by a laser beam source, to a scanning member such as a galvano mirror, etc. and projecting the scanned beam to the subject's retina, and a light receiving optical system for taking out the light reflected by the eye fundus through a common optical path with the illuminating optical system.
In case the eye fundus of a patient is going to be observed or photographed using such the eye fundus camera as mentioned, the central portion of the eye fundus is usually observed and/or photographed in many cases. However, there are some cases where the peripheral portion of the eye fundus is desired to be observed and/or photographed.
As a method for observing and/or photographing the peripheral portion of the eye fundus, several methods are considered such as, for example, a method for spreading an angle of view by attaching a contact lens to the subject's eye, a method for spreading the range of observation and/or photographing by changing the reference scanning position of a galvano mirror and without changing the angle of view of an optical system, etc.
However, in the method using a contact lens, it is required to drop an anesthetic lotion in the subject's eye in order to dilate the pupil thereof. This renders a heavy burden onto a patient. In addition, there is a fear of getting infection.
Also, in the method for changing the reference scanning position of a galvano mirror, although the range of observation and photographing can be spread to some extent, it is impossible to observe and/or photograph the peripheral portion of the eye fundus due to limitation of an objective lens in size.
Therefore, heretofore, the whole eye fundus camera was tilted upwardly or downwardly to tilt the optical axis of the eye fundus camera with respect to the optical axis of the eye when the peripheral portion of the eye fundus was going to be observed and/or photographed.
However, since the eye fundus camera is heavy, it is not easy to tilt the camera.
Also, as an eye fundus camera of a laser beam scanning type, there is one in which a polygon mirror is rotated at a high speed to scan illuminating beam in the horizontal direction and a galvano mirror scans the horizontally scanned scanning beam in the vertical direction.
Since the polygon mirror of this type of eye fundus camera is rotated at a high speed, it produces a gyroscopic moment. As a result, when the eye fundus camera is about to be tilted vertically, the camera is tended to return to its original posture position due to the function of the gyro moment, thus making it difficult to tilt the camera in the desired direction rapidly and easily. Moreover, in case an air bearing is used as a bearing for this polygon mirror, there is a risk that the rotary shaft of the polygon mirror and the bearing are contacted with each other, thus resulting in breakage thereof. Also, when the whole eye fundus camera is to be tilted in the vertical direction as described, the rotary shaft of the polygon mirror is tilted and load incurred to the bearing of the polygon mirror is one-sided. This results in a cause of one-sided wear of the bearing and thus not desirable.